Rolling bearing

ABSTRACT

When a minimum thickness of a part where an outer ring raceway is provided on a middle portion in the axial direction of an outer ring is h, and a diameter of each rolling element is Da, the relationship 0.4 Da≦h 0.8 Da is satisfied. As a result, even when the outer ring  4   a  is fixed in a transmission case of low-rigidity, elastic deformation of the outer ring can be prevented without needlessly increasing the thickness h of the outer ring. 
     When an outer diameter of an outer ring is D, a width of this outer ring in the axial direction is W, a minimum thickness of a part where the outer ring raceway is provided on a middle portion in the axial direction of the outer ring is h, and a diameter of each ball is Da, the respective dimensions are controlled such that a value K calculated by {(h 1.5 ·W)/(Da 1.1 ·.D 0.5 )} satisfies the relationship 1.20≦K≦2.00. As a result, sufficient rigidity of the outer ring can be maintained, and early exfoliation based on elastic deformation of the outer ring can be prevented without needlessly increasing the size of the outer ring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ensuring durability of rolling bearingsfor rotatably supporting rotating members of various rotating machineryand equipment such as pulleys on automobile alternators and belt-typecontinuously variable transmissions, and gears and the like constitutingmanual transmissions and automatic transmissions.

2. Description of the Related Art

Firstly, rolling bearings using a low-viscosity CVT fluid (including ATFcompatible oil), and incorporated into transmission cases of lowrigidity are described.

As disclosed in, for example, Japanese Examined Utility ModelPublication No. H8-30526 and the like, a variety of belt-typecontinuously variable transmissions has been heretofore designed asspeed changing units in automatic transmissions for automobiles, andsome of these have been employed in practice. FIG. 1 shows the basicstructure of such a belt-type continuously variable transmission insimplified form. This belt-type continuously variable transmission hasan input rotating shaft 1 and an output rotating shaft 2 which aremutually arranged in parallel. These rotating shafts 1 and 2 arerotatably supported within a transmission case (not shown in drawings),which is a fixed part, by respective pairs of rolling bearings 3.

As shown in detail in FIG. 2, each rolling bearing 3 has a concentricouter ring 4 and an inner ring 5. The outer ring 4 has an outer ringraceway 6 on an inner peripheral face, and the inner ring 5 has an innerring raceway 7 on an outer peripheral face. A plurality of rollingelements 8 are rotatably provided between the outer ring raceway 6 andthe inner ring raceway 7 while being held by a retainer 9. In therolling bearings 3 which are respectively constructed in this manner,the outer ring 4 is fixed to the inside of part of the transmissioncase, and the inner ring 5 is fixed on the outside of the input rotatingshaft 1 or the output rotating shaft 2. Both of these rotating shafts 1and 2 are rotatably supported within the transmission case by thisconstruction. The outer ring 4, the inner ring 5, and the rollingelements 8 manufactured of general class 2 bearing steel (SUJ2), haveconventionally been used for each rolling bearing 3.

Of the rotating shafts 1 and 2, the input rotating shaft 1 is driven torotate by a drive source 10 such as an engine via a start clutch 11 suchas a torque converter or electromagnetic clutch. Furthermore, a drivepulley 12 is provided at a part positioned between the pair of rollingbearings 3 in the middle portion of the input rotating shaft 1, so thatthis drive pulley 12 and the input rotating shaft 1 rotatesynchronously. By displacing one drive pulley plate 13 a (on the left inFIG. 1) in the axial direction with a drive actuator 14, the spacebetween the pair of drive pulley plates 13 a and 13 b constituting thedrive pulley 12 can be freely adjusted. That is to say, the width of thegroove in the drive pulley 12 can be freely increased or decreased withthe drive actuator 14.

On the other hand, a driven pulley 15 is provided at a part positionedbetween the pair of rolling bearings 3 in the middle portion of theoutput rotating shaft 2, so that this driven pulley 15 and the outputrotating shaft 2 rotate synchronously. By displacing one driven pulleyplate 16 a (on the right in FIG. 1) in the axial direction with a drivenactuator 17, the space between the pair of driven pulley plates 16 a and16 b constituting the driven pulley 15 can be freely adjusted. That isto say, the width of the groove in the driven pulley 15 can be freelyincreased or decreased with the driven actuator 17. An endless belt 18is spanned between the driven pulley 15 and the drive pulley 12. Forthis endless belt 18, a metal belt is used.

In the belt-type continuously variable transmissions constructed asdescribed above, the drive transmitted from the drive source 10 to theinput rotating shaft 1 via the start clutch 11 is transmitted from thedrive pulley 12 to the driven pulley 15 via the endless belt 18.Heretofore as the endless belt 18, there is known one wherein drive istransmitted in the push direction, and one wherein drive is transmittedin the pull direction. In either case, the drive transmitted to thedriven pulley 15 is transmitted to a drive wheel 21 from the outputrotating shaft 2 via a reduction gear train 19, and a differential gear20. When changing the gear ratio between the input rotating shaft 1 andthe output rotating shaft 2, the groove width of the pulleys 12 and 15is increased or decreased while changing the relationship between thetwo.

For example, to increase the speed reduction ratio between the inputrotating shaft 1 and the output rotating shaft 2, the width of thegroove in the drive pulley 12 is increased, and the width of the groovein the driven pulley 15 is decreased. As a result, the diameter of theparts of the pulleys 12 and 15 spanned by part of the endless belt 18 isdecreased on the pulley 12, and increased on the pulley 15, and speedreduction is performed between the input rotating shaft 1 and the outputrotating shaft 2. Conversely, to increase the speed increasing ratiobetween the input rotating shaft 1 and the output rotating shaft 2(decrease the speed reduction ratio), the width of the groove of thedrive pulley 12 is decreased, and the width of the groove of the drivenpulley 15 is increased. As a result, the diameter of the parts of thepulleys 12 and 15 spanned by part of the endless belt 18 is increased onthe pulley 12, and decreased on the pulley 15, and speed increase isperformed between the input rotating shaft 1 and the output rotatingshaft 2.

When operating the belt-type continuously variable transmissionconstructed and operating as described above, lubricating oil issupplied to each moving part to lubricate each moving part. Thelubricating oil employed in the belt-type continuously variabletransmission is CVT fluid (including ATF compatible oil). The reason forthis is to increase and stabilize the coefficient of friction of thefrictional engagement parts of the metal endless belt 18 and the driveand driven pulleys 12 and 15. The CVT fluid is circulated to thefrictional engagement parts at a flow rate of at least 300 cc per minuteto lubricate these frictional engagement parts. Moreover, part of theCVT fluid is passed through the interior of each of the rolling bearings3 (for example, at a flow rate of at least 20 cc per minute) tolubricate the rolling contact parts of the rolling bearings 3. Thereforethere is a high possibility that foreign matter such as wear particlesgenerated by wear accompanying frictional between the endless belt 18and the pulleys 12 and 15, and gear dust generated by friction in thereduction gear train 19, will become mixed with the CVT fluid and enterthe interior of these rolling bearings 3. Such foreign matter may damagethe rolling contact parts of the rolling bearings 3, and reduce theirdurability.

Therefore, heretofore the bearing size of the rolling bearings 3 hasbeen increased, or the diameter Da of the rolling elements 8 has beenincreased, to increase the basic dynamic load rating of the rollingbearings 3, and to provide a margin for the life of the rolling bearings3. However, when in this manner the diameter Da of the rolling elements8 is increased to maintain the basic dynamic load rating, a thickness Tof the outer ring 4 must be reduced (made thinner) to reduce the sizeand weight of the belt-type continuously variable transmission.Furthermore, when the rigidity of the transmission case securing theouter ring 4 is low, if the thickness T of this outer ring 4 is reducedin this manner, elastic deformation of the outer ring 4 occurs readily,and an excessive bending stress is applied to the outer ring 4accompanying the deformation, so that there is a possibility that thelife of the rolling bearings 3 will be reduced.

For example, in the Proceedings of the Tribology Conference of theJapanese Society of Tribologists (Morioka 1992-10) E-33, pp 793-796, itis disclosed that the life of this rolling bearing was reduced by ¼ to ⅕when the rolling bearing was operated with a bending stress of 70 MPaapplied to the raceway ring, in comparison to the case where a bendingstress was not applied. Furthermore, it is disclosed that, in order toprevent such a reduction in life, manufacture of the raceway ring from amaterial wherein a residual compression stress has been applied iseffective. However, in order to employ the material wherein such aretained compression stress has been applied, carburized steel must beemployed in the raceway ring, and mechanical processes such asshot-peening and the like must be applied to the raceway face of theraceway ring, with the possibility of increased cost.

Recently, in order to ensure the efficiency of belt-type continuouslyvariable transmissions, to suppress noise generated during operation,and to suppress wear of the drive and driven pulleys 12 and 15, and theendless belt 18, the use of a fluid of lower viscosity is underconsideration as a CVT fluid. In this case, if standard rolling bearingsare employed as the rolling bearings 3 to support the input and outputrotating shafts 1 and 2, the possibility of premature flaking isconsidered to increase. That is to say, the action of vibration in theradial and axial directions accompanying belt fluctuations exacerbateselastic deformation of the outer ring 4 and the inner ring 5, and anexcessive bending stress is applied to the outer ring 4 and the innerring 5. Accompanying this deformation and excessive bending stress,metal-to-metal contact based on sliding, occurs more readily in therolling contact parts between the outer ring raceway 6 and the innerring raceway 7, and the rolling contact surfaces of the rolling elements8, and the possibility of premature flaking of the outer ring raceway 6,the inner ring raceway 7, and the rolling contact surfaces of therolling elements 8 increases due to such metal-to-metal contact.

That is to say, there are cases where the temperature of the rollingbearing 3 during operation of the belt-type continuously variabletransmission may exceed 100° C. At this time the kinetic viscosity ofthe CVT fluid which enters the interior of the rolling bearing 3 andlubricates the rolling contact parts of the rolling bearing 3 isconsiderably low at 10 mm² per second or less. Moreover, there is also apossibility of a tendency for the amount of CVT fluid supplied to therolling contact parts to become insufficient. Furthermore, when therigidity of the transmission case, being the fixed part, is low, theouter ring 4 fixed to the transmission case is readily elasticallydeformed, and sliding based on differential movement, revolution, andspinning of the rolling elements 8 occurs readily in the rolling contactparts accompanying this deformation. As a result, together with the lackof CVT fluid as described above, the oil film on the rolling contactparts readily breaks up. When the oil film breaks up in such a manner,the outer ring raceway 6 and the rolling contact surfaces of the rollingelements 8 enter an activated state wherein surface fatigue associatedwith, for example, hydrogen embrittlement flaking due to hydrogenpenetration, and metal-to-metal contact, is accelerated, and thepossibility of premature flaking increases.

On the other hand, according to Hertz' theory of elastic contact, themaximum shear stress under rolling contact is calculated to occur at adepth from the raceway face of approximately 2% of the diameter of therolling element. In this case, the thickness of the raceway ring whereinthe maximum shear stress occurs is calculated as being semi-infinite. Onthe other hand, in the case of a standard JIS name and number's rollingbearing, the thickness of the raceway ring tends to be set approximatelyten times the depth from the raceway face to the position where themaximum shear stress occurs, that is to say, approximately 20% of thediameter of the rolling element 8. The reason for this is that, when theraceway ring is fixed to a highly rigid part, if the thickness of thisraceway ring is approximately 20% of the diameter of the rollingelement, the Hertz' theory of elastic contact wherein the thickness ofthis raceway ring is considered as semi-infinite is established.Moreover, it is considered that experimentally sufficient durability canbe maintained. Therefore, in the case of the rolling bearing 3incorporated in the belt-type continuously variable transmission, if therigidity of the transmission case is low, the thickness of the outerring 4 fixed to this transmission case must be increased (made thicker)to ensure durability of the rolling bearing 3. However, simplyincreasing the thickness of the outer ring 4 in this manner invitesincreased weight associated with increased size, and increased rollingresistance. Therefore it is not desirable.

In Japanese Unexamined Patent Publication No. H10-37951, there isdisclosed an invention for improving the permissible high-speedperformance of rolling bearings used for machine tools, by increasingthe thickness of the outer ring in comparison to the thickness of theinner ring. That is to say, a construction is disclosed wherein ceramicrolling elements are used to thereby reduce the centrifugal forceapplied to the outer ring, being the fixed raceway ring. Moreover, inorder to reduce the centrifugal force generated in the inner ring, beingthe rotating raceway ring, the thickness of this inner ring is made 2.5mm to 4.0 mm, and the thickness of the outer ring is 2.0 to 2.75 timesthe thickness of the inner ring. However, with this structure, thepurpose of making the thickness of the outer ring greater than thethickness of the inner ring is simply to reduce the centrifugal force byreducing the thickness of the inner ring, and not to prevent elasticdeformation of the outer ring fixed to the low-rigidity part. Moreover,since the rolling elements are made of ceramic, increased materialscosts and machining costs cannot be avoided. Furthermore, since thethickness of the outer ring is excessive, the rolling contact surfacesof the rolling elements are readily damaged, as described later.

Next is a description of a rolling bearing fixed to an alternator havinga low-rigidity housing made for example from aluminum alloy.

In various auxiliary equipment having as a power source the drive engineof an automobile, a rotating shaft is rotatably supported in relation tothe housing, and a driven pulley is fixed to one end of this rotatingshaft on a portion projecting from the housing. The various auxiliaryequipment can be freely driven by transmitting the rotation of theengine crankshaft to this driven pulley via an endless belt. FIG. 3shows an example of an alternator which generates electric powernecessary for an automobile, being one of such various auxiliaryequipment. In this alternator 101 a rotating shaft 103 is rotatablysupported inside a housing 102 made from a light metal such as aluminumalloy, by a pair of rolling bearings 104. Each of these rolling bearings104 comprises an inner ring 106 having an inner ring raceway 105 formedon an outer peripheral surface, an outer ring 108 having an outer ringraceway 107 formed on an inner peripheral surface, and a plurality ofballs 109 being rolling elements, rotatably arranged between the innerring raceway 105 and the outer ring raceway 107.

Moreover, a rotor 110 and a commutator 111 are provided in the middleportion of the rotating shaft 103. Furthermore, a driven pulley 112 isfixed to an end part of the rotating shaft 103 projecting from thehousing 102. With the housing 102 fixed to the engine (not shown indrawings), an endless belt (not shown in drawings) is wrapped around thedriven pulley 112, so that the rotation of the crankshaft of the enginecan be freely transmitted to the rotating shaft 103 via the endlessbelt. Moreover, a stator 113 is fixed to a part surrounding the rotor110 on the inside of the housing 102. In the alternator 101 constructedin this manner, the rotating shaft 103 provided with the rotor 110 isrotated by the rotation of the engine, and electric current is generatedin the stator 113 facing this rotor 110.

When the alternator 101 constructed as described above is in use, whilethe inner rings 106 constituting the rolling bearings 104 rotate, aradial load is continuously applied in the same direction to the innerrings 106 based on the tension of the endless belt. When such a radialload is applied to the outer rings 108 via the balls 109, and therigidity of the housing 102 securing the outer rings 108 is low, thereis a possibility that the outer rings 108 may elastically deformtogether with the housing 102. Such elastic deformation of the outerrings 108 is considered to be a cause of damage such as prematureflaking of the outer rings 108.

That is to say, it is considered that, when the outer rings 108elastically deform together with the housing 102 based on the radialload, this radial load is applied to the outer ring 108 as an unbalancedload, and the outer rings 108 vibrate more readily. Under such anunbalanced load and vibration, it becomes more difficult to form an oilfilm of lubricant such as grease or lubricating oil on the rollingcontact parts between the inner ring raceway 105 and the outer ringraceway 107 and the rolling contact surface of each ball 109.Furthermore, if the lubricant contains water, or if moisture penetratesfrom the outside, there is also a possibility that formation of an oilfilm on the rolling contact parts will become more difficult. When itbecomes difficult to form an oil film on the rolling contact parts inthis manner, metal-to-metal contact occurs more readily between theinner ring raceway 105 and the outer ring raceway 107, and the rollingcontact surface of the balls 109, and there is a possibility ofpremature flaking of the inner ring raceway 105, the outer ring raceway107, and the rolling contact surface of the balls 109.

Inventions are disclosed to prevent such premature flaking in, forexample, Japanese Unexamined Patent Publication No. 2001-221238 whereinthe constituents of the material of the outer ring are controlled, andin Japanese Unexamined Patent Publication No. H5-98280 wherein theconstituents of the grease are controlled. However, with the rollingbearings incorporated into auxiliary equipment (electrical components)for automobiles, such as alternators and electromagnetic clutches,conditions of use have become more severe with the effects of increasedtemperature and speed due to improvements in engine performanceassociated with recent technical innovations, and increased loadsassociated with increase in belt tension. Therefore mere control of thecomponents constituting the rolling bearings and the lubricant is nolonger sufficient to accommodate these changes in conditions of use, andthe possibility of a reduced life due to premature flaking has appeared.

SUMMARY OF THE INVENTION

The present invention provides a rolling bearing for use in belt-typecontinuously variable transmissions wherein damage such as prematureflaking and the like to the outer ring raceway, the inner ring raceway,and the rolling contact surfaces of the rolling elements constitutingthe rolling contact parts does not occur readily, even when the outerring is fixed to a transmission case of low-rigidity material such asaluminum alloy.

The rolling bearing of the present invention comprises an outer ring, aninner ring, and a plurality of rolling elements.

Of these, the outer ring has an outer ring raceway on its innerperipheral surface.

Moreover, the inner ring has an inner ring raceway on its outerperipheral surface.

Furthermore, the rolling elements are rotatably provided between theouter ring raceway and the inner ring raceway.

The outer ring is fitted into and supported inside a fixed part of atransmission case, and the inner ring is fitted onto and supported on apart which rotates together with a pulley constituting the belt-typecontinuously variable transmission, such as the end or an intermediatepart of input and output rotating shafts, so that the pulley isrotatably supported on the fixed part.

In particular, in the rolling bearing for use in belt-type continuouslyvariable transmissions, when the minimum thickness (thickness in theradial direction) of the part where the outer ring raceway is providedon the central portion in the axial direction of the outer ring is h,and the diameter of the rolling elements is Da, the relationship 0.4Da≦h≦0.8 Da, or more desirably, 0.4 Da≦h≦0.6 Da, is satisfied.

In the rolling bearing for use in belt-type continuously variabletransmissions of the present invention constructed as described above,sufficient flaking life can be maintained, even if a low-viscosity CVTfluid is used, and the rolling bearing is incorporated into alow-rigidity transmission case.

That is to say, even when the outer ring is fixed to a low-rigiditytransmission case made of aluminum alloy for example, elasticdeformation of the outer ring, and application of excessive stress onthe outer ring accompanying this deformation can be prevented, withoutneedlessly increasing the thickness of the outer ring. Therefore even incases where, due to using a low-viscosity CVT fluid, or not circulatinga large volume of lubricating oil (for example, a volume greatlyexceeding 20 cc per minute) inside of the rolling bearing, it isdifficult to maintain the strength of an oil film on the rolling contactparts between the outer ring raceway and the inner ring raceway, and therolling contact surface of the rolling elements, it is possible toprevent metal-to-metal contact in these rolling contact parts, and tomaintain sufficient flaking life. It is therefore no longer necessary toincrease the size of the rolling bearing in order to maintain thenecessary durability, so that the rotating support parts of the inputrotating shaft and the output rotating shaft can be made small andlight-weight, and turning resistance can be reduced. As a result, thebelt-type continuously variable transmission can be reduced in size andweight, and transmission efficiency can be improved.

In particular, in the rolling bearing incorporated into auxiliaryequipment (electrical components) for automobiles such as alternatorsand electromagnetic clutches, if the outer diameter of the outer ring isD, the width in the axial direction of this outer ring is W, the minimumthickness of the part where the outer ring raceway is provided on thecentral portion in the axial direction of the outer ring is h, and thediameter of the rolling elements is Da, the relationship1.20≦{(h^(1.5)·W)/(Da^(1.1)·D^(0.5))}≦2.00 is satisfied.

According to the rolling bearing of the present invention constructed asdescribed above, even if the outer ring is fixed to a low-rigidityhousing made of a light metal such as aluminum alloy, sufficientrigidity of the outer ring can be maintained, and premature flakingbased on elastic deformation of the outer ring can be prevented, withoutneedlessly increasing the size of the outer ring, and consequently therolling bearing.

That is to say, if the rigidity of the housing is low, the outer ringelastically deforms together with the housing to an extent which cannotbe ignored, and the load zone is reduced. That is to say, the outer ringis elastically deformed such that it is expanded outwards in the radialdirection around the part wherein the load is applied, and the expandedpart can no longer support the load. Therefore there is a tendency forthe load to be concentrated at the part where the load is applied. Ifthe rolling elements enter the part where the load is concentrated inthis manner from the non-load zone, a constraining force is appliedabruptly to these rolling elements (the extent of constraint increasesconsiderably), and severe slippage occurs readily between the rollingcontact surfaces of the rolling elements and the outer ring raceway andthe inner ring raceway. The oil film formed on the rolling contact partsbetween the rolling contact surfaces of the rolling elements and theinner ring raceway and the outer ring raceway then readily breaks downaccompanying this slippage, and metal-to-metal contact occurs readilybetween the rolling contact surfaces of the rolling elements and theinner ring raceway and the outer ring raceway. Moreover, also if therolling elements spring out from the load zone, since they are suddenlyreleased from a large constraining force, slippage occurs in the samemanner, and metal-to-metal contact occurs readily accompanying thisslippage. Premature flaking then occurs readily in the rolling contactparts between the rolling contact surfaces of the rolling elements andthe inner ring raceway and the outer ring raceway based on thismetal-to-metal contact. If the rigidity of the housing is low, the outerring raceway also readily deforms elastically (such that the peripheralgroove forms a wave-shape in the radial direction ) based on the loadfrom the rolling elements in (passing through) the load zone. Theslippage also occurs readily due to elastic deformation of the racewayface in this manner, and may accelerate premature flaking.

Therefore the thickness h and the width W of the outer ring areoptimized so that as mentioned above, these are controlled to1.20≦{(h^(1.5)·W) /(Da^(1.1)·D^(0.5))}≦2.00, and elastic deformation ofthe outer ring does not occur readily, and premature flaking due to themechanism described above is thus prevented. If the value calculated inthe expression {(h^(1.5)·W)/(Da^(1.1)·D^(0.5))} (hereafter referred toas ‘K’) is less than 1.20, the rigidity of the outer ring is too low,and if the outer ring is fixed to a low-rigidity housing made ofaluminum alloy or the like, elastic deformation of the outer ring occursreadily and flaking as described above may occur at an early stage. Onthe other hand, if K exceeds 2.00, the rigidity of the outer ring may betoo high, so that when the rolling elements are assembled into therolling bearing, deformation of the outer ring exceeds the range ofelastic deformation, so that plastic deformation occurs and the outerring is damaged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified section view of a drive system of an automobileincorporating a belt-type continuously variable transmission comprisingrolling bearings being the object of the present invention.

FIG. 2 is one example of an enlarged view showing a removed rollingbearing.

FIG. 3 is a simplified section view showing an example of a heretoforeknown alternator.

FIG. 4 is section view similar to FIG. 2, showing an example of anembodiment of the present invention.

FIG. 5 is a partial section view showing an example of the embodiment ofthe present invention.

FIG. 6 is a diagram schematically showing load applied to an outer ringvia rolling elements, in the case of a high-rigidity housing.

FIG. 7 is a diagram schematically showing load applied to the outer ringvia rolling elements, in the case of a low-rigidity housing.

FIG. 8 is a graph showing the results of an experiment conducted toverify effects.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 4 shows an example of an embodiment of the present invention. Acharacteristic of the present invention is that a structure is devisedfor a rolling bearing 3 for supporting input and output side rotatingshafts 1 and 2 (see FIG. 1) for a belt-type continuously variabletransmission, so that even when the rigidity of a transmission case islow, sufficient durability of the rolling bearing 3 is maintained. Sincethe structure and operation of other parts, including the structureshown in FIG. 2, are similar to the heretofore known rolling bearingsfor belt-type continuously variable transmissions, equivalent parts aredenoted by the same reference symbols, and duplicated description isomitted or simplified. Hereunder, the description focuses oncharacteristic parts of the present invention.

In the present example, when the minimum thickness (thickness in theradial direction) of the part where the outer ring raceway 6 is providedon the middle portion in the axial direction of the outer ring 4 is h,and the diameter of the rolling elements 8 is Da, the dimensions of theouter ring 4 are controlled so that the relationship 0.4 Da≦h≦0.8 Da, ormore desirably, 0.4 Da≦h≦0.6 Da, is satisfied. Furthermore, the width Win the axial direction of the outer ring 4 and the inner ring 5 iscontrolled within a range which satisfies 1.2 Da≦W≦2.5 Da. In the caseof the rolling bearing 3 in the present example, sufficient flaking lifecan be maintained, even if a low-viscosity CVT fluid is used and therolling bearing is incorporated into a low-rigidity transmission case.

That is to say, even when the outer ring 4 is fixed to a light-weightand low-rigidity transmission case such as of aluminum alloy, elasticdeformation of the outer ring 4, and application of excessive stress onthe outer ring 4 accompanying this deformation, can be prevented withoutneedlessly increasing the thickness h of the outer ring 4. Thereforeeven in cases where, due to using a low-viscosity CVT fluid, or notcirculating a large volume of lubricating oil (for example, volumesgreatly exceeding 20 cc per minute) inside of the rolling bearing 3, itis difficult to maintain the strength of an oil film on the rollingcontact parts between the outer ring raceway 6 and the inner ringraceway 7, and the rolling contact surface of the rolling elements 8, itis possible to prevent metal-to-metal contact in these rolling contactparts, and to maintain sufficient flaking life. It is therefore nolonger necessary to increase the size of the rolling bearing 3 in orderto maintain the necessary durability, so that the rotating support partsof the input rotating shaft 1 and the output rotating shaft 2 can bemade small and light-weight, and turning resistance can be reduced. As aresult, the belt-type continuously variable transmission can be reducedin size and weight, and transmission efficiency can be improved.

If the minimum thickness h of the outer ring 4 a exceeds 0.8 Da, therolling elements 8 are not readily assembled into the rolling bearing 3.That is to say, when the rolling bearing 3 is assembled using automaticassembly equipment, the rolling elements 8 which are normally assembledlast, are assembled into the rolling bearing with the outer ring 4elastically deformed. Therefore, if the minimum thickness h exceeds 0.8Da, the load required to elastically deform the outer ring 4 increases,so that the outer ring 4 and the rolling elements 8 may be readilydamaged, and it may no longer be possible to assemble using automaticassembly equipment. On the other hand, if the minimum thickness h isless than 0.4 Da, and if the rigidity of the transmission case whichsecures the outer ring 4 is low, the outer ring 4 is readily elasticallydeformed, and premature flaking may occur on the outer ring raceway 6and the inner ring raceway 7, and the rolling contact surfaces of therolling elements 8.

Moreover, the width W in the axial direction of the outer ring 4 andinner ring 5 is desirably as large as possible to prevent elasticdeformation of the outer ring 4 and the inner ring 5. However, if thewidth W is increased, the mass of the outer ring 4 and the inner ring 5is also increased. That is to say, if the width W exceeds 2.5 Da, themass of the outer ring 4 and the inner ring 5 become too large, and thetransmission efficiency of the belt-type continuously variabletransmission may be reduced. On the other hand, if the width W is lessthan 1.2 Da, the rigidity of the outer ring 4 and the inner ring 5 isreduced, and the outer ring 4 and the inner ring 5 may readilyelastically deform. It is therefore desirable that the width W be keptwithin a range of 1.2 Da or greater and 2.5 Da or less.

Furthermore, in the present example, no sealing members are provided inthe openings at both ends of the part where the plurality of rollingelements 8 are provided between the inner peripheral surface of theouter ring 4 and the outer peripheral surface of the inner ring 5.However, when there is a high possibility of entry of a significantamount of foreign matter such as wear particles from the drive anddriven pulleys 12 and 15 and the endless belt 18 (see FIG. 1), it isdesirable that a sealing member be provided, provided that thedimensions in the axial direction of the rolling bearing permit this. Assuch a sealing member, in addition to a light-contact type oftransmission seal, a non-contact type seal made of metal plate, or anitryl seal or acryl seal or fluorine seal of a contact type or anon-contact type and the like can be selected to use in consideration ofthe temperature in use.

Moreover, the construction and the material of the retainer 9 whichrotatably holds the rolling elements 8 is not particularly limited.However when the rotational speed in use is particularly high, the useof a crown type retainer made of synthetic resin is desirable to reducefriction between the retainer and the rolling elements, and to suppressthe generation of hard wear particles, thus extending life. On the otherhand, in cases where rupture of the retainer may occur due to the actionof a large variable load, use of a metal waveform retainer is desirable.

Furthermore, in the present example, the outer ring 4, the inner ring 5,and the rolling elements 8 constituting the rolling bearing 3 are madeof class 2 bearing steel (SUJ2) wherein the amount of retained austeniteγ_(R) is 5 to 15 volume %. However, when there is a large amount offoreign matter inside the belt-type continuously variable transmission,mixed with the CVT fluid, and passing through the installation space ofthe rolling elements 8 of the rolling bearing 3, it is desirable thatthe steel constituting the outer ring 4, the inner ring 5, and therolling elements 8 be at least partially carburized or carbonitrided. Ifthe amount of retained austenite in the surfaces of the outer ring 4,the inner ring 5, and the rolling elements 8 is 20 to 45 volume %, andthe surface hardness is approximately (H_(R) C 62 to 67) with suchtreatment, damage to these surfaces by foreign matter can be preventedand the durability of the rolling bearing 3 can be increased. Moreover,when the temperature of the rolling bearing 3 in use reaches 150° C. ormore, it is desirable that a dimension stabilizing treatment whichsuppresses retained austenite to approximately 0 to 5% be applied to theouter ring 4, the inner ring 5, and the rolling elements 8. In thiscase, it is desirable that a heat-resistant rubber be used as thesealing member.

Furthermore, in the present example, the internal clearances of therolling bearing 3 are normal clearances, and the radius of curvature ofthe cross-section of the outer ring raceway 6 and the inner ring raceway7 is 0.52 times the diameter of the rolling elements 8 (0.52 Da) in allcases. However if the internal clearances and radius of curvature of thecross-section of the raceways 6 and 7 are appropriately controlled (keptsmall; for example, the radius of curvature of the inner ring raceway 7is controlled to at least 0.505 Da), the radius of curvature of theouter ring raceway 6 is controlled to 0.535 Da, a backlash in the radialdirection and backlash in the axial direction are suppressed, and thecontact pressure between the rolling contact surfaces of the rollingelements 8 and the outer ring raceway 6 and inner ring raceway 7 is madeuniform, then durability-related performance may be further increased.Moreover, regarding the rolling bearing 3, the operation and effectsobtained are not limited to the single-row deep-groove type ball bearingas shown in the drawings, and may also be obtained with other types ofball bearings such as angular types, and additionally with cylindricalroller bearings and tapered roller bearings, needle bearings, and otherbearings.

EXAMPLES

Next is a description of an experiment conducted to verify the effectsof the present invention. In the experiment, as shown in the followingTable 1, durability was respectively measured on a total of 14 samples:ten samples (examples 1 through 10) being within the technical scope ofthe present invention wherein the minimum thickness h of the outer ring4 was between 0.4 and 0.8 times the diameter Da of the rolling elements(balls) 8, and four samples (comparative examples 1 through 4) beingoutside the technical scope of the present invention. These samples werebased on JIS name-number 6209 (inner diameter d=45 mm, outer diameterD=85 mm, width W=19 mm, ball diameter Da=11.906 mm) and JIS name-number6310 (inner diameter d=50 mm, outer diameter D=110 mm, width W=27 mm,ball diameter Da=11.906 mm) ball bearings, and were adjusted to thedimensions noted in Table 1 below by respectively varying the outsidediameter of each outer ring and the diameter of the balls.

TABLE 1 Outer ring Outer outer ring Ball L₁₀ diameter thickness diameterlife Presence of D [mm] h [mm] Da [mm] h [hr] damage Other Example 1 875 11.906 0.42 Da 500 5/5 normal 6209 2 89 6 0.50 Da 500 5/5 normal base3 91 7 0.59 Da 500 5/5 normal 4 93 8 0.67 Da 500 1/5 ball damage 5 95 90.76 Da 500 2/5 ball damage 6 117 8 19.050 0.42 Da 500 5/5 normal 6310 7119 9 0.47 Da 500 5/5 normal base 8 121 10 0.53 Da 500 5/5 normal 9 12311 0.58 Da 500 5/5 normal 10 125 12 0.63 Da 500 1/5 ball damage Comp. 185 4 11.906 0.34 Da 97 5/5 outer ring 6209 example flaking (std) 2 97 100.84 Da 125 5/5 ball 6209 flaking base 3 110 4.5 19.050 0.23 Da 84 5/5outer ring 6310 flaking (std) 4 113 6 0.31 Da 91 5/5 outer ring 6310flaking base

Rolling bearings 3 of the dimensions noted in the Table 1 wererespectively incorporated in a belt-type continuously variabletransmission as shown in FIG. 1, and employed to rotatably support theinput rotating shaft 1 in relation to the transmission case. Thearithmetic average roughness Ra of each surface constituting the rollingcontact part was between 0.01 and 0.03 μm as with normal rollingbearings. Furthermore, the bearing material was standard class 2 bearingsteel (SUJ2, hardness=H_(R) C 60 to 65). Moreover, steel waveformpressing retainers were employed as the retainer 9. Furthermore, therolling elements (balls) 8 were of SUJ2, through hardening and annealed,and then finished by grinding and super-finishing.

A durability test was conducted with a target time of 500 hours underthe conditions described below. Following completion of the test, therolling bearings 3 were dismantled and the component parts of therolling bearings 3 were checked for damage, and the L₁₀ life (ratedfatigue life) was calculated. In the current experiment, in order toobtain the durability of the rolling bearings 3 incorporated in therotating support part of the input rotating shaft 1, a sufficient amount(200 cc per minute) of lubricating oil (CVT fluid) was supplied to therolling bearings 3 incorporated in the rotating support part of theoutput rotating shaft 2. Moreover care was taken to ensure that rollingbearings 3 not tested would not be damaged before tested rollingbearings 3 would be damaged.

Test conditions were as follows.

Test equipment: Belt-type continuously variable transmission shown inFIG. 1. Number of test samples: Five of each sample. Method ofevaluation: Dismantled after 500 hours running, however testdiscontinued immediately and bearing dismantled if vibration valueincreased rapidly during the test. Input torque from engine to 250 N · m(bearings in accordance with or input rotating shaft 1: based on JISname-number 6209), and 500 N · m (bearings in accordance with or basedon JIS name-number 6310) Rotational speed of input 6000 min⁻¹ rotatingshaft 1: Lubricating oil: CVT fluid {dynamic viscosity at 40° C. = 35mm² per sec = 35 × 10⁻⁶ m² per sec (35 cSt), viscosity at 100° C. = 7mm² per sec = 7 × 10⁻⁶ m² per sec (7 cSt)} Lubricating oil flow rate: 10cc per minute Bearing temperature: 120° C.

The ratio of engine torque and basic dynamic load rating of rollingbearing was approximately the same for all rolling bearings.

The following points were understood from the results of the experimentconducted under the above conditions.

Firstly, in all examples 1 through 10 within the technical scope of thepresent invention, operation was able to be continued without damage tothe rolling bearings 3 until they reached the target 500 hours.Moreover, of these, examination of the raceway surfaces of examples 1through 3 and examples 6 through 9 after the test revealed thatpolishing traces remained and the state of lubrication was satisfactory.Furthermore, no damage based on creep was apparent on the outerperipheral surface of the outer ring 4.

On the other hand, damage to the rolling elements (balls) 8 was found inexamples 4, 5, and 10. This damage was considered to be due to the factthat the outer ring 4 did not readily elastically deform when therolling elements (balls) 8 were assembled into the rolling bearings 3,due to the thickness h of the outer ring 4 being large enough.Consequently it was understood that the rolling elements 8 should not bereadily damaged when assembling such rolling bearings 3, and it is moredesirable that the thickness h of the outer ring be 0.4 Da to 0.6 Da(0.4 Da≦h≦0.6 Da).

Moreover, premature flaking occurred (after 84 to 125 hours) in therolling contact parts, and severe vibration was generated in all thecomparative examples 1 through 4 outside the technical scope of thepresent invention. Furthermore, of these, examination of the racewaysurfaces of comparative examples 1 and 3 revealed that part of thepolishing traces had not remained, and it was considered that localizedmetal-to-metal contact had occurred. Moreover, damage to the outerperipheral surface of the outer ring 4 based on creep was apparent, andit was considered that slippage of the rolling elements 8 occurred inthe load zone of the outer ring based on this creep. Furthermore, sincethe thickness h of the outer ring 4 of the comparative example 2 was toogreat at 0.84 Da, it was considered that premature flaking occurred atthe point of damage occurring when the rolling elements (balls) 8 wereassembled into the rolling bearing 3. Moreover, since the thickness h ofthe outer ring 4 of the comparative example 4 was too small at 0.31 Da,similarly to the comparative examples 1 and 3, damage based onmetal-to-metal contact in the rolling contact parts accompanying elasticdeformation of the outer ring 4 was apparent on the outer ring raceway6.

FIG. 5 shows another example of an embodiment of the present invention.The rolling bearing 104 of the present example being a deep-groove typeball bearing comprises an inner ring 106 being a rotating ring formedwith an inner ring raceway 105 on the outer peripheral face, an outerring 108 being a fixed ring formed with an outer ring raceway 107 on theinner peripheral face, and a plurality of balls 109 being rollingelements rotatably arranged between the inner ring raceway 105 and theouter ring raceway 107. Furthermore, sealing rings 114 are provided inthe openings at both ends of the part where the plurality of balls 109are provided between the inner peripheral surface of the outer ring 108and the outer peripheral surface of the inner ring 106.

In particular, with the rolling bearing 104 of the present example, ifthe outer diameter of the outer ring 108 is D, the width in the axialdirection of this outer ring 108 is W, the minimum thickness of the partwhere the outer ring raceway 107 is provided on the middle portion inthe axial direction of the outer ring 108 is h, and the diameter of theballs 9 is Da, the respective dimensions are controlled so that thevalue K calculated by {(h^(1.5)·W)/(Da^(1.1)·D^(0.5))} satisfies therelationship 1.20≦K≦2.00.

According to the rolling bearing 104 of the present example constructedas described above, even if the outer ring 108 is fixed to alow-rigidity housing made of light metal such as aluminum alloy,sufficient rigidity of the outer ring 108 can be maintained, andpremature flaking based on elastic deformation of the outer ring 108 canbe prevented, without needlessly increasing the size of the outer ring108, and consequently the rolling bearing 104.

That is to say, research by the inventor of the present invention hasshown that, if the rigidity of the housing is low, the outer ring 108elastically deforms together with the housing to an extent which cannotbe ignored, and premature flaking occurs due to such elasticdeformation. Specifically, when the rigidity of the housing securing theouter ring 108 is high, if a load is applied to the rolling bearing, aload distribution from each ball 109 becomes as shown by the arrows inFIG. 6. On the other hand, when the rigidity of this housing is low, theload distribution from each ball 109 becomes as shown by the arrows inFIG. 7. As is apparent from FIG. 6 and FIG. 7, when the rigidity of thehousing is high, an average load is applied to the outer ring 108 from alarge number of balls 109 (a large load zone), however, when therigidity of the housing is low, the load is applied to the outer ring108 concentrated from a small number of balls 109 (small load zone).That is to say, the outer ring 108 is elastically deformed such that itis expanded outwards in the radial direction around the part where theload is applied (lowermost point of radial load zone), and since theexpanded part can no longer support the load, there is a tendency forthe load to be concentrated at the part wherein the load is applied. Ifthe balls 109 enter the part wherein the load is concentrated in thismanner from the non-load zone, a constraining force is applied abruptlyto these balls 109 (the extent of constraint increases considerably),and severe slippage occurs readily between the rolling contact surfacesof the balls 109 and the outer ring raceway 107 and the inner ringraceway 105.

The oil film formed in the rolling contact parts between the rollingcontact surfaces of the balls 109 and the inner ring raceway 105 and theouter ring raceway 107 then readily breaks down in association with thisslippage, and metal-to-metal contact occurs readily between the rollingcontact surfaces of the balls 109 and the inner ring raceway 105 andouter ring raceway 107. Moreover, also if the balls 109 spring out fromthe load zone, since they are suddenly released from a largeconstraining force, slippage occurs in the same manner, andmetal-to-metal contact occurs readily accompanying this slippage.Premature flaking then occurs readily in the rolling contact partsbetween the rolling contact surfaces of the balls 109 and the inner ringraceway 105 and the outer ring raceway 107 based on this metal-to-metalcontact. If the rigidity of the housing is low, the outer ring raceway107 readily deforms elastically (such that the peripheral groove forms awave-shape in the radial direction) based on the load from the balls 109in (passing through) the load zone. The slippage also occurs readily dueto elastic deformation of the raceway surface in this manner, and mayaccelerate premature flaking. Furthermore, the metal-to-metal contactoccurs more readily with high levels of vibration, high temperatures,and increased water in the lubricating oil and water mixed due tocondensation and the like.

Therefore the thickness h and the width W of the outer ring 108 areoptimized so that as mentioned above, the value K calculated by{(h^(1.5)·W)/(Da^(1.1)·D^(0.5))} is controlled to within a range of1.20≦K≦2.00, and elastic deformation of the outer ring 108 does notoccur readily, and premature flaking due to the mechanism describedabove is thus prevented. That is to say, application and release ofconstraint of the balls 109 is comparatively gradually performed at bothends in the load zone, and the premature flaking is prevented. If K isless than 1.20, the rigidity of the outer ring 108 is too low, and ifthe outer ring 108 is fixed to a low-rigidity housing made of aluminumalloy or the like, elastic deformation of the outer ring 108 occursreadily and flaking as described above may occur at an early stage. Onthe other hand, if K exceeds 2.00, the rigidity of the outer ring 108may be too high, so that when the balls 109 are assembled into therolling bearing 104, deformation of the outer ring 108 exceeds the rangeof elastic deformation, so that plastic deformation occurs and the outerring 108 is damaged.

Moreover, the inventor of the present invention also focused on thecreep of the outer ring 108 rotating in the same direction as thedirection of rotation of the inner ring 106 based on the rotatingresistance of the rolling bearing 104. It was then understood that byoptimizing the thickness h and width W of the outer ring 108 asdescribed above so that elastic deformation of the outer ring 108 doesnot occur readily, premature flaking as described above and creep of theouter ring can be prevented. That is to say, it was understood that byensuring rigidity of the outer ring 108, a localized increase in thesurface pressure between the outer ring 108 and the housing can besuppressed, and creep of the outer ring due to this localized increasein the surface pressure can be prevented.

Next is a description of an experiment conducted to verify the effectsof the present invention. In the experiment, durability of the samplesrespectively shown in the following Table 2 and Table 3 was measured. InTable 2 and Table 3, samples within the technical scope of the presentinvention were examples 11 through 16, and samples outside the technicalscope of the present invention were comparative examples 5 through 8.Furthermore, respective samples shown in Table 2 below were based on JISname-number 6204 (inner diameter d=20 mm, outer diameter D=47 mm, widthW=14 mm, ball diameter Da=7.937 mm, minimum thickness h of outerring=2.781 mm) deep-groove type ball bearings of standard class 2bearing steel (SUJ2), and samples shown in Table 3 were based on JISname-number 6207 (inner diameter d=35 mm, outer diameter D=72 mm, widthW=17 mm, ball diameter Da=11.112 mm, minimum thickness h of outerring=3.694 mm) deep-groove type ball bearings of standard class 2bearing steel (SUJ2), and the value K calculated by{(h^(1.5)·W)/(Da^(1.1)·D^(0.5))} was adjusted by respectively varyingthe outer diameter D of each outer ring.

TABLE 2 Test Outer diameter of K = {(h^(1.5) · W)/ Sample time outerring D [mm] (Da^(1.1) · D^(0.5))} No. [hr] Compar- Φ47 0.97 1 265 ative2 303 example 3 211 5 4 335 5 198 Compar- Φ47.5 1.10 1 358 ative 2 387example 3 432 6 4 500← 5 455 Example Φ48 1.22 1 500← 11 2 465 3 500← 4500← 5 500← Example Φ48.5 1.36 1 500← 12 2 500← 3 500← 4 500← 5 500←Example Φ49 1.51 1 500← 13 2 500← 3 500← 4 500← 5 500←

TABLE 3 Test Outer diameter of K = {(h^(1.5) · W)/ Sample time outerring D [mm] (Da^(1.1) · D^(0.5))} No. [hr] Compar- Φ72 1.01 1 388 ative2 452 example 3 546 7 4 420 5 553 Compar- Φ72.5 1.11 1 486 ative 2 580example 3 530 8 4 670 5 710← Example Φ73 1.21 1 710← 14 2 710← 3 710← 4682 5 710← Example Φ73.5 1.31 1 710← 15 2 710← 3 710← 4 710← 5 710←Example Φ74 1.42 1 710← 16 2 710← 3 710← 4 710← 5 710←

Durability tests of the rolling bearings of the respective dimensionsnoted in Table 2 and Table 3 were then conducted with a target time of500 hours (Table 2) and 710 hours (Table 3) under the conditionsdescribed below, and time until flaking occured was investigated. Thereason for setting the target times as above was so that the L₁₀ life(rated fatigue life) under the conditions of the experiment was 494hours (Table 2) and 705 hours (Table 3). Moreover, in the currentexperiment, inner ring rotation was with the outer ring fixed to thehousing and the inner ring rotated. Furthermore, with the samples inTable 2, sealing rings were provided in the openings at both ends of thepart where the plurality of balls were provided between the innerperipheral surface of the outer ring and the outer peripheral surface ofthe inner ring, and lubrication was with grease. Moreover, with thesamples in Table 3, no sealing rings were provided, and the openings atboth ends of the part where the plurality of balls were provided wereleft open, and forced lubrication was employed by making lubricating oilcirculate through this part.

Test conditions were as follows.

(1) Table 2 samples: Number of test samples Five of each sample.Internal clearance: C3 Radius of curvature of inner 52% of ball diameterring raceway and outer ring raceway: Load: P (bearing load)/C (dynamicload rating) = 0.15 Rotational speed of 10000 min⁻¹ inner ring:Lubricant: EA2 grease, enclosed capacity 35% Ambient temperature: 100°C. Water content of grease: 1 weight % of grease (2) Table 3 samplesNumber of test samples: Five of each sample. Internal clearance: C3Radius of curvature of inner 52% of ball diameter ring raceway and outerring raceway: Load: P (bearing load)/C (dynamic load rating) = 0.15Rotational speed of 7000 min⁻¹ inner ring: Lubricant: ATF fluid {dynamicviscosity at 40° C. = 35 mm² per sec = 35 × 10⁻⁶ m² per sec (35 cSt),dynamic viscosity at 100° C. = 7 mm² per sec = 7 × 10⁻⁶ m² per sec (7cSt)} Oil temperature: 100° C. Water content of grease: 1 weight % (30cc) in 3 l of lubricating oilThe following points were understood from the results of the experimentconducted under the above conditions.

Firstly, in Table 2, in comparative example 5 (D=47 mm, k=0.97) havingthe standard outer diameter of outer ring and being outside thetechnical scope of the present invention, no sample reached thecalculated life (L₁₀ life) of 494 hours, and premature flaking occurred.On the other hand, the majority (14 of 15) of samples in examples 11through 13 within the technical scope of the present invention satisfiedthe calculated life. Even if the outer diameter D of the outer ringexceeded 49 mm, it was found that premature flaking could be prevented.However, if the outer diameter D of the outer ring exceeded 51 mm(K=2.10), that is to say, when K exceeds 2.00, the outer ringplastically deforms when assembling the balls into the rolling bearing,and hence this is not desirable.

Furthermore, in Table 3, in the comparative example 7 (D=72 mm, k=1.01)having the standard outer diameter of outer ring and being outside thetechnical scope of the present invention, no sample reached thecalculated life (L₁₀ life) of 705 hours, and premature flaking occurred.On the other hand, the majority (14 of 15) of samples in examples 14through 16 within the technical scope of the present invention satisfiedthe calculated life. Even if the outer diameter D of the outer ringexceeded 74 mm, it was found that premature flaking could be prevented.However, if the outer diameter D of the outer ring exceeded 77 mm(K=2.11), that is to say, when K exceeds 2.00, the outer ringplastically deforms when assembling the balls into the rolling bearing,and hence this is not desirable.

The relationship between the life of the rolling bearing and the K valueis shown in FIG. 8. As is apparent from FIG. 8, even when the outer ringis fixed to a low-rigidity housing made of aluminum alloy or the like,the outer ring is not readily elastically deformed and sufficient lifecan be maintained, by controlling K to 1.20 to 2.00.

INDUSTRIAL APPLICABILITY

Since the rolling bearing of the present invention for use in belt-typecontinuously variable transmissions is constructed and operates asdescribed above, sufficient durability can be maintained even if alow-viscosity CVT fluid is employed, and the outer ring is fixed in atransmission case having a low-rigidity. It is therefore possible toincrease the efficiency of belt-type continuously variable transmissionswhile maintaining durability.

Moreover, since the present invention is constructed and operates asdescribed above, even when the outer ring is fixed in a low-rigidityhousing made of aluminum alloy or the like, premature flaking can beprevented, contributing to increased durability of various rotatingmachinery and equipment incorporating the rolling bearing, withoutneedlessly increasing the size of the outer ring. The invention isparticularly suitable for the case of supporting a rotating shaftprovided with a pulley or gear such as with an alternator or atransmission, in a housing made of a low-rigidity material such asaluminum alloy as described above, and can contribute to increaseddurability and reliability of such an alternator or transmission.

1. A rolling bearing for vehicle comprising: an outer ring having anouter ring raceway on an inner peripheral surface; and an inner ringhaving an inner ring raceway on an outer peripheral surface; and aplurality of rolling elements rotatably provided between the outer ringraceway and the inner ring raceway, and when a minimum thickness of apart where the outer ring raceway is provided on a middle portion in theaxial direction of the outer ring is h, and a diameter of each rollingelement is Da, the relationship 0.4 Da≦h≦0.8 Da is satisfied.